The present invention relates to a push-button switch and, in particular, to a push-button switch having a simple structure for overload protection and automatic reset.
There are many types of push-button switches for various applications, such as one having a turn-on indicating lamp and one provided with an overload protection function. In terms of one having an overload protection function, there are also several kinds of protection principles or mechanisms being adopted. For example, both the blow-out of a fuse wire and the tonal deformation of a bimetal blade have ever been adopted as a trigger source for an overload protection. However, the fuse wire is not repetitive and thus its utility rate gradually decreases. As for the thermal bimetal blade, there are many kinds of mechanism, such as is those disclosed in U.S. Pat. Nos. 5,786,742, 5,223,813, 4,937,548, 4,661,667, 4,931,762, 5,451,729, and 4,704,594.
For example, in the U.S. Pat. No. 5,786,742, a so-called power-cutting member (72) used to alternatively set a set and a reset positions of a switch is disclosed. In that case, a bimetallic blade (75) is used to push a shaft seat (71) to trip and automatically reset a switch. However, the contacts in such a switch are directly depressed by a button. Thus, if the button has jammed or pushed down by an external force, they would be kept in its conducting position even if overload occurs. Moreover, such a switch is not economical because of a use of up to four contacts to construct a conducting circuit. The possibility of generating an arc also increases. Furthermore, such a switch is troublesome to provide a wire connecting the bimetallic blade (75) with the conducting plate (74).
In U.S. Pat. No. 5,223,813, a bimetal beam (13), a common trip (17) actuated by the bimetal beam, and a cam member (27) are incorporated with a rocker actuator (33) to perform a contact between contact members (7,1). In such a switch, the common trip (17) will result in a displacement in response to the deformation of the bimetal beam so as to release the cam member and to trip the switch. Since the common trip is indirectly actuated by a rocker actuator, a jamming of the rocker actuator and a neglectful re-push on the switch after overload can be avoided. However, such a switch is rather complicated. Moreover, since it needs a wire to be connected between its cantilever spring (5) and its bimetal beam (13), its assembly is also troublesome. Furthermore, a fail-action could possibly happen when overload occurs since the bimetal beam may be not able to simultaneously actuate the rocker actuator (33) and the common trip (17).
In U.S. Pat. No. 4,937,548, a circuit breaker which utilizes the deformation of a thermal actuator (76) to displace a lock lever (62) so as to release a bell crank lever operator (52) is disclosed. In this case, a movable contact (86) is indirectly actuated by the actuator, and thus a jamming of the actuator and a re-push on the switch in case of overload can be avoided. However, such an arrangement is not provided with an automatic resetting function, and an indicating lamp is difficult to install therein. In U.S. Pat. No. 4,661,667, a double-heart-shaped cam locking mechanism is used to obtain two locking-positions. However, such a switch lacks an overload protection function as well as a status-indicating function.
A main object of the present invention is to provide a push-button switch having a simple structure easy to assemble and having a low manufacturing cost.
Another object of this invention is to provide a push-button switch having an overload protection mechanism capable of exactly and transiently operating at a critical point of overload.
Yet another object of this invention is to provide a push-button switch having an automatic resetting mechanism for simultaneously resetting the switch in case of overload.
To achieve the above objects of this invention, this invention provides a push-button switch with overload protection and automatic reset, comprising:
a housing;
a conducting unit installed in the housing and including a first terminal, a second terminal, a first conducting leaf, and a flat bimetal sheet; the bimetal sheet having a movable working end, being able to move to an overload position from a normal position in case of overload, and a fixed opening end formed with first and second legs for respectively connecting with the first terminal and the first conducting leaf; the first conducting leaf being movable between a closed position in which the second leg of the bimetal sheet is electrically connected to the second terminal and a normal-open position in which the second leg is disconnected from the second terminal;
an acting unit installed in the housing and including:
a stem provided with a heart-shaped stepping recess and being able to slidably move between an upper reset position and a lower set position;
a locating cantilever provided with a first hand pivotally mounted at the housing and a second hand movably inserted into the heart-shaped stepping recess for locating the position of the stem;
a rocking lever pivotally supported on the stem along a shaft and formed with a nose for depressing the first conducting leaf and with a resting tail opposite to the nose across the shaft;
an enabling rest capable of moving between a supporting position to support the resting tail and a withdrawing position to withdraw from the resting tail, in correspondence with the location of the bimetal sheet in the normal position and the overload position, respectively;
a cantilever pusher for pushing the locating cantilever away from the heart-shaped stepping recess in response to the change of the bimetal sheet into its overload position; and
a lever reseating member for pushing the rocking lever into an idle position in which the resting tail could be supported by the enabling rest during a reset course in which the stem moves from the set position to the reset position;
whereby the nose can depress and release the first conducting leaf so as to make the first conducting leaf move into the closed position and the normal-open position in response to the movement of the stem to its set position and its reset position, respectively, in a situation that the enabling rest locates in its supporting position, and whereby the first conducting leaf and the stem can move to its normal-open position and its reset position, respectively, in response to a change of the bimetal sheet into its overload position.
By means of the above structure, even if the stem jams, the switch can still exactly and transiently trip at the time overload occurs. Moreover, by virtue of the cantilever pusher, the switch could be automatically reset after overload occurs and thus make the procedure to operate the switch simple.
In a preferred embodiment, the working end of the bimetal sheet deflects away from the resting tail upon overload and has a side edge and an end edge, and the enabling rest is integrally formed with the bimetal sheet on the side edge and formed with a platform on which the resting tail can rest.
By means of the special structure of the bimetal sheet, a protection mechanism having a simpler structure with more elasticity is available and thus its assembly becomes easier.